In the process of manufacturing semiconductors, an adhesive sheet has hitherto been used for protecting the circuit-formed side of semiconductor wafers at the stage of polishing the back side of the wafers; while, at the dicing stage, it has so far been used for fixing semiconductor wafers to ring frames for dicing. In the former case of using an adhesive sheet for protection, pieces having the same shape as the semiconductor wafers to be protected have been cut from the adhesive sheet. In the latter case of using an adhesive sheet for the dicing, circular pieces with a diameter including the ring frame diameter and a margin to paste up have been cut from the adhesive sheet.
As for the cutting of an adhesive sheet for protection or dicing, there have been known two methods; one method is a pre-cut method wherein a base film having thereon an adhesive layer protected by a release liner is punched in advance so that pieces of the base film with the intended shape are arranged in series and laminated on the release liner via the adhesive layer, and the other method is a batch cut process wherein a roll of long adhesive sheet is prepared without cutting out any unnecessary part and, at the time of use, the unnecessary part is cut out with a cutter so as to leave necessary pieces. The batch cut process requires that the adhesive sheet be fed so as to keep enough distance for the cutting operation. As the part corresponding to this feed distance is useless, the necessary area of an adhesive sheet per silicon wafer becomes larger. Therefore, the batch cut process is inferior in productivity.
According to the pre-cut method, an adhesive sheet used in the process of manufacturing semiconductors, which has a resinous base film laminated via the adhesive layer on a long piece of release liner, is cut from the side of the base film into the surface of the release liner by means of, e.g., a die cutter, and then the base film in the unnecessary part is removed together with the adhesive layer from the release liner to leave only the necessary part of the adhesive layer covered with the base film (hereinafter referred to as the adhesive film) on the release liner.
In storing the thus processed long piece of adhesive sheet, the sheet is cut properly into short pieces of adhesive sheets, and these pieces are superposed one upon another. In another way of storing, the processed long piece of adhesive sheet is wound into a roll. At the time of practical use in the course of manufacturing semiconductors, e.g., at a dicing stage, the pre-cut adhesive film is peeled apart from the release liner and applied to a semiconductor wafer or the like.
However, when the adhesive sheet as the finished product is a roll of the adhesive sheet having only the precut adhesive film on the release liner, it frequently happens that (i) the adhesive sheet is wound in a state that it slips sideways every turn to form a roll having a shape like a bamboo shoot, (ii) the adhesive is forced out of the adhesive film present in the vicinity of the core by the wind pressure, or/and (iii) the adhesive film surface is rendered rough with increase in the winding diameter because adhesive films cannot be superposed, but come to overlap each other and bear the stamp of each other's contour, which causes pitching or damage to chips upon dicing. Thus, inferior goods are liable to be produced in such a case.
If the wind pressure is therefore made lower, it becomes harder to keep the adhesive sheet in roll shape at the time of transportation or use, so that the control of wind pressure is troublesome. On the other hand, when the adhesive films released from the adhesive sheet which was rolled up as it slipped sideways are applied to substrates, it frequently happens that those adhesive films leave part of the adhesive on the substrates when they are peeled away. Such foreign matter left on the substrates is referred to as adhesive deposit. The generation of adhesive deposit becomes a fatal defect of an adhesive sheet, particularly when the adhesive sheet is used in the process of manufacturing semiconductor.
In a case where the pre-cut adhesive sheet is stored in roll shape, it has a drawback of suffering the collection of dust in the gaps formed by cutting off the adhesive film on the both side parts of the roll. In another case where the pre-cut adhesive sheet is stored or transported in a state that it is cut into equal pieces so that every piece has one adhesive film and these pieces are superposed upon one another, the same trouble as mentioned above is caused. In addition to such a dust trouble, the sheet pieces superposed have a defect that it is difficult to automatically feed them to semiconductor wafers.
Therefore, it is also carried out that, after the precuts are made in an adhesive sheet to the depth of the adhesive film, the adhesive sheet is forwarded without removing therefrom unnecessary part of the adhesive film and placed at users' disposal. In this case, however, the necessary and unnecessary parts of the adhesive layer which have once been cut apart come to adhere again to each other with a lapse of time under wind pressure or the like. Thus, easy and exact release of only the necessary part of the adhesive film from the adhesive sheet becomes impossible at the time of use.
Accordingly, it is also put in practice to cut off the adhesive film in an appropriate width on the borders of the necessary part and the unnecessary part. Even if the adhesive sheet is wound into a roll or cut into equal pieces and superposed in such a case, the wind or superposition pressure does not concentrate in a particular part of the adhesive sheet; as a result, the necessary part of the adhesive film suffers neither damage nor deformation and the adhesive layer is prevented from being forced out. In this case, therefore, the necessary part of the adhesive film is peeled apart from the release liner with certainty.
Further, the adhesive sheet stored in a rolled or superposed state is free from the adhesion of dust because it has no gaps in side parts.
However, it frequently occurs in the adhesive sheet of such a type that the partial delamination of the adhesive film is caused even in the part to be left on the release liner upon removal of the adhesive film on the border of the necessary part and the unnecessary part in the course of the production thereof. This phenomenon makes it difficult to continuously produce adhesive sheets of this type. In addition, the disposal of unnecessary part as waste becomes necessary.
In recent years, the tendency to reduce the amount of wastes has been strengthened in conformity with ISO 14001, so that in the case of forwarding the adhesive sheets in a roll form, the recycling and regeneration of roll cores have begun to be required. Thus, new cost is added to the production cost.